Due to potential applications in smart systems, materials that sense external stimuli and execute responses that enhance overall system functionality are attractive areas for research. While some of these materials undergo reversible changes upon application of an external stimulus, others undergo irreversible changes. Examples of such stimuli-responsive materials include piezoelectrics, ferroelectrics, shape-memory alloys, electrostrictive materials, dielectric elastomers, liquid crystal elastomers, and conducting polymers. Despite, and in part because of, individual strengths and weaknesses, these materials have been implemented to fulfill various sensing and actuation roles in industrial smart systems.
In this regard, a decade of nanotube/polymer composite research has yielded a number of insights into the molecular design and mechanical properties of nanocomposites. Carbon nanotube fillers have been used to increase strength; as stress recovery agents in thermoplastic elastomers and IR actuators; to improve damping capability; as shape/temperature memory composites; as space durable films for electrostatic charge mitigation; to improve flammability resistance; as conductive scaffolds for printable composites and gels; as electro-responsive chromatic materials; and as skin-like pressure and strain sensors. The combination of high strength, light weight, and large elastic energies in these composites have been proposed for diverse applications ranging from high-end sports equipment to artificial muscles in humanoid robots. While important, many of these applications, however, merely incorporate nanotubes to accentuate already existing host matrix features (such as strength, toughness, conductivity), and there has been little success in the development of stimuli-responsive composites that exhibit dynamic changes in strength, conductivity, density, and volume (visible on macroscopic scales).